1. Field of the Invention
The present invention relates to a hybrid compressor system for a refrigeration cycle system mounted in a hybrid vehicle or an idle-stop vehicle which is designed not to idle for long periods of time.
2. Description of the Related Art
Generally, hybrid or idle-stop vehicles are commercially available to address the increasing need for fuel efficient vehicles which is intended to decrease the overall consumption of fuel. In these vehicles, the engine is adapted to stop in some running states (e.g., during rest stops for the idle-stop vehicle while, and for the hybrid vehicle, during rest stops, running at low speeds, and during starts or initial vehicle motion). The engine stopping causes the compression unit in a refrigeration cycle system, which is driven by the engine, to stop which ceases to provide air conditioning for the passenger compartment.
To address this problem, for example, there is disclosed in Japanese Patent Laid-Open Publication No. 2000-130323, a hybrid compressor in which rotation of the engine causes a pulley and a compression unit to be coupled to each other via an electromagnetic clutch with a rotating shaft of the compression unit opposite to the pulley being coupled with a motor. With this configuration, the motor can drive the compression unit when the electromagnetic clutch is turned OFF when the engine is stopped. This permits the refrigeration cycle system to operate even when the engine is stopped, thereby providing cooling for the vehicle.
However, considering the technique disclosed in the patent mentioned above, suppose the motor is to be responsible for the operation of the compression unit so as to achieve the maximum cooling capacity required of the refrigeration cycle system when the engine is stopped. In this case, it is necessary to provide both a motor and an external power supply of increased size, though it is only practical to employ a motor of a moderate size in consideration of ease of mounting the motor and all associated costs. This also requires the engine to run when cooling is lacking, which results in diminished fuel economy compared to what was originally expected.
Furthermore, the technique of the patent publication mentioned above is adapted to allow the motor to drive the compression unit only when the engine is stopped. Accordingly, this additional motor is not intended for use in response to all possible conditions of the vehicle, thereby causing the problems identified below to remain unsolved.
For instance, while the engine is running, variations in the rotation speed of the engine cause the compression unit to vary in operation, resulting in an unstable flow of the refrigerant. This degrades the efficiency of the refrigeration cycle system. Of greater concern is that this can lead to degradation of the fuel efficiency of the engine, as well as deterioration of the vehicle compartment environment which includes vibration and noise developed in the passenger compartment arising from the operational variations of the compression unit and the engine.
It is possible to alleviate the reduced efficiency of the refrigeration cycle system, due to variations in the rotational speed of the engine, by employing a variable volumetric capacity type compression unit to adjust the amount of discharge. However, this would make the compression unit itself expensive and cause a drop in the efficiency of the compression unit when it is operated at a reduced capacity of its variable volumetric capacity, thereby resulting in a degradation of the fuel economy of the engine.
On the other hand, a motor-driven compression unit is also known that does not need to be driven by an engine (e.g., Japanese Patent Laid-Open Publication No. Hei 11-159338). Arguably, the motor-driven compression unit makes it possible to avoid the influence exerted by variations in the rotational speed of the engine during operation. However, this motor-driven compression unit requires the motor to be sized in consideration of the maximum cooling capacity (as mentioned above) of the compression unit, thereby making it necessary to increase the sizes of both the motor and the external power supply.